Method of spray coating gas seals of gas turbines and the like



United States Patent Int. Cl. $23k 9/04; C22c 19/00; C0911 /10 U.S. Cl.219-76 2 Claims ABSTRACT OF THE DISCLOSURE A method, especially usefulfor coating the gas seals :of gas .turbines, in which mixtures ofpowders are sprayed, by means of a plasma arc gun, onto the surface tobe coated, under temperature conditions such that one of the powders ismelted or partially melted to provide a matrix, and the other powderremains unmelted, but the particles thereof are held tightly in thematrix, to supply a soft material in an otherwise hard mass.

This application is a continuation-in-part of my co pending application,Ser. No. 459,075,, filed May 26, 1965, now abandoned.

This invention relates generally to methods for coating gas seals of gasturbines, and for other purposes.

In Patent No. 3,265,494, of James F. Baldwin and Arthur T. Cape, analloy is described, known as Coast Metals No. 64, which is a cobalt-basealloy containing substantial amounts of chromium, tungsten and nickel.The alloy is especially adapted for high temperature use, as, forexample, for coating the gas seal of a gas turbine. The alloy has amelting point of about 2500 F., and a hardness of 50-60 Rockwell C, andwhen deposited on such seal is so hard that the turbine blades becomeworn as a result of their rubbing against the deposit.

I have found that if the foregoing alloy, in powder form, is mixed withcobalt, in powder form, to the extent that the cobalt powder constitutesfrom to 60% by weight of the mixture, that the mixture, when sprayed bya plasma arc gun onto the gas seal, forms a coating which consists ofunmelted cobalt particles held in a matrix of the alloy, which coatingis of such a nature that it greatly reduces the wear of the turbineblades. The coating has a hardness of about 35-40 Rockwell C.

In spraying the mixture by means of a plasma arc gun, the alloyparticles are melted, or partially melted, but the cobalt particlesremain unmelted, and are held tightly in the matrix formed by the alloyparticles. In eflect, the cobalt particles supply a soft material, in anotherwise hard mass, thus reducing the tendency to wear the ends of theturbine blades.

The coating is thus highly desirable, not only from the viewpoint ofadherence to the gas seal, but also from the viewpoint of reducing thewearing or cutting of the turbine blades.

Although it is preferred to use cobalt powder in the mixture, powdersother than cobalt may be used, such, for example, as tungsten powder,chromium powder, nickel powder, molybdenum powder, and iron powder, theonly limitation, in this respect, being that such powder have a meltingpoint higher than that of the No. 64 alloy, and the property of notreacting rapidly with the molten or semi-molten N0. 64 during thedeposition.

The invention is applicable generally to all cobalt-base alloyscontaining chromium and tungsten, with or without 3,436,512 PatentedApr. 1, 1969 nickel. Examples of such alloys are Coast Metals No. 63,Stellite No. 1, Stellite No. 6.

The invention is also of advantage in all applications where the alloysper se are as hard as those described, but the addition of the cobalt orother powder provides a coating in which the high temperature propertiesof the alloy per se are retained while maintaining the advantages of adeposit more able to withstand impact, without deterioration of theresistance of the deposit to lead oxide corrosion or oxidation.

For example, the invention is applicable to the facing of the seatingportions of poppet valves, especially those which are used in internalcombustion engines.

It will be understood that various changes may be made in the methods,without departing from the spirit of the invention or the scope of theappended claims.

Having thus described my invention, I claim:

1. The method which comprises spraying onto a surface to be coated, bymeans of a plasma arc gun, a mixture consisting of (A) a first powder ofa cobalt-base alloy containing chromium and tungsten, and (B) a secondpow der selected from the group consisting of cobalt powder, tungstenpowder, chromium powder, nickel powder, and iron powder, in an amountconstituting from 15% to 60% by weight of the mixture, the melting pointof the first powder being lower than the melting point of the secondpowder, the spraying being conducted under temperature conditions suchthat the cobalt-base alloy powder is melted or partially melted, but theother powder remains unmelted and the particles thereof are held tightlyin a matrix of the melted or partially melted material, and supply asoft material, in an otherwise hard mass.

2. The method which comprises spraying onto the gas seal of a gasturbine, by means of a plasma arc gun, a mixture consisting of (A) afirst powder of a cobaltbase alloy containing chromium and tungsten, and(B) a second powder selected from the group consisting of cobalt powder,tungsten powder, chromium powder, nickel powder, and iron powder, in anamount constituting from 15% to 60% by weight of the mixture, themelting point of the first powder being lower than the melting point ofthe second powder, the spraying being conducted under temperatureconditions such that the cobalt-base alloy powder is melted or partiallymelted, but the other powder remains unmelted, and the particles thereofare held tightly in a matrix of the melted or partially melted material,and supply a soft material, in an otherwise hard mass, thereby reducingthe tendency to wear the ends of the turbine blades when rubbing againstsaid coated gas seal.

References Cited UNITED STATES PATENTS 3,000,755 9/1961 Hanink et a1117-131 X 3,035,934 5/1962 Cape 117-22 3,249,428 5/1966 Weisman -1713,265,494 8/1966 Baldwin et al 75-171 3,310,423 3/1967 Ingham 219-76 X3,313,633 4/1967 Longo 106-1 3,322,546 5/1967 Tanzman et a1 117-1052 X3,362,816 1/1968 Winter et al 75-171 FOREIGN PATENTS 672,841 10/1963Canada.

RICHARD M. WOOD, Primary Examiner. C. L. ALBRITTON, Assistant Examiner.

US. Cl. X.R. 75-170, 171, 176; 106-1; 117-22, 93,

